1. Field of the Invention
The present invention relates to an electromagnetic valve which is installed in a fluid pressure circuit for e.g. an anti-lock braking device.
2. Description of the Related Art
The electromagnetic valve as an electromagnetic driving component is generally provided with a coil unit with a coil winding wound around a bobbin and a valve operating unit for opening/closing the valve by passing a current through or energizing the coil unit. Such an electromagnetic valve includes a normally-closed electromagnetic valve which is normally closed but opened when the valve operating unit is operated by energizing the coil unit, and a normally opened electromagnetic valve which is normally opened but closed when the valve operating unit is operated by passing a current through the coil unit. These electromagnetic valves are selectively employed according a purpose and use.
A normally-closed electromagnetic valve has been proposed which is used for a braking device for a motor vehicle. For example, the normally-closed electromagnetic valve is fit in a guide sleeve with an air gap remaining between a magnetic core (fixed core) and a movable piece (movable core) and coupled with the guide sleeve by a ring-shaped welding portion. The solenoid coil is designed to open when the movable piece is moved by energizing a solenoid coil fit outside the magnetic core (see JP-W-9-506309).
Otherwise, another electromagnetic valve structure has been proposed in which a sleeve is arranged on the inner periphery of a solenoid coil, an armature core is fixed to the one end of the sleeve whereas an valve seat is fixed to the other end of the sleeve. A movable seat which is normally urged is seated between the armature core and valve seat. In this electromagnetic valve structure, the one end of the sleeve which is inserted in the solenoid coil and welded to the armature core is tapered to improve the combining capability with a valve body (see Japanese Patent No. 3236540)
In the normally-closed electromagnetic valve disclosed in the JP-W-9-506309, the magnetic core (fixed core) is press-fitted into the one end of the guide sleeve inserted in the solenoid coil and fixed by welding. A bead of welding is therefore formed so as to swell on the outer periphery of the guide sleeve. Due to the bead, a gap between the guide sleeve and the coil bobbin is created, so that the solenoid coil is large-scaled.
Further, in the electromagnetic valve structure disclosed in the Japanese Patent No. 3236540, the one end of the sleeve welded to the armature core inserted in the solenoid coil is tapered. The electromagnetic valve structure must be therefore assembled in such a manner that from the one end of the sleeve, the armature core is press-fitted whereas from the other end of the sleeve, a compressed coil spring, movable piece, valve seat, etc. are inserted. In this way, the electromagnetic valve structure is assembled from both ends of the sleeve so that the assembling process becomes complicate.
An object of this invention is to solve the problem of the above prior arts and to provide an electromagnetic valve which does not excessively large-scale electromagnetic driving components to improve assembling capability.
In order to solve the above problems, this invention has the following constructions.
According to a first aspect of the present invention, it is provided that an electromagnetic valve having: a coil unit including a bobbin around which a coil winding is wound, the bobbin having a central hole; a pipe body in which a fixed core is press-fitted and welded; and a valve operating unit with the pipe body inserted in the central hole of the bobbin at an one end thereof, a valve of the valve operating unit being opened or closed when the coil unit is energized, wherein, in an inserted portion of the pipe body opposed to the central hole of the bobbin, a welding portion in which a fixed core is welded is formed in a thin-wall sectional shape reduced only an outer diameter thereof, and a difference in the outer diameter between the welding portion and the inserted portion serves to absorb the swelling of a bead due to the welding.
According to a second aspect of the present invention, it is provided that the electromagnetic valve according to the first aspect further having: a movable core mounted in the pipe body in such a manner that a spring is interposed between the movable core and the fixed core, and including a valve body disposed at a tip of the movable core; and a valve seating member mounted in the other end of the pipe body, wherein the valve body is always seated at a valve seating member thereby closing the valve, and when the coil unit is energized, the movable core is sucked toward the fixed core against the urging by the spring, thereby opening the valve.
According to a third aspect of the present invention, it is provided that the electromagnetic valve according to the second aspect, wherein a bottom edge portion is integrally formed at the other end of the pipe body against which the end of the valve seating member is hit.
According to a fourth aspect of the present invention, it is provided that the electromagnetic valve according to the first aspect, wherein a pipe body including a top portion and mounting a movable core in vicinity of the top portion, the fixed core mounting a valve seating member and a valve shaft, the valve shaft including a valve body disposed at a tip thereof and disposed in such a manner that a spring is interposed between the valve shaft and the valve seating member, the rear end of the valve shaft is kept in contact with a movable core in such a manner that the valve body is always apart from the valve seating member, thereby opening the valve, and when the coil unit is energized, the movable core is sucked toward the fixed core so that the rear end of the valve shaft is pushed against the urging by the spring, thereby closing the valve.
According to a fifth aspect of the present invention, it is provided that the electromagnetic valve according to the first aspect, wherein an inner diameter of the inserted portion of the pipe body is constant.
According to a sixth aspect of the present invention, it is provided that the electromagnetic valve according to the first aspect, wherein the welding portion formed in the thin-wall sectional shape includes tapered portions so as to form a concave groove.